This invention pertains generally to fire control systems, and particularly to systems of such type whereby the trajectory of a cannon-launched projectile is controlled during flight.
It has been proposed that a so-called "beam-riding" technique be used to control the flight path of a cannon-launched projectile such as an artillery shell. Thus, in the system described in U.S. Pat. No. 4,300,736 (assigned to the same assignee as the present application), the relative rotational motion between a modulated beam of infrared (IR) energy and a spinning projectile is used to determine, during flight, the displacement of such a projectile from the center-line of such beam so that the trajectory of the projectile may be corrected as required to enable a selected target to be hit. Unfortunately, however, due to atmospheric disturbances as, for example, fog or smoke, the modulated beam and its spatial pattern may become distorted, or diffused, with the result that proper location of the projectile at the center of the beam is difficult to achieve. Furthermore, because of the uncertainty in the initial position of the projectile (such uncertainty being due to the ballistic dispersion of the cannon) a relatively broad beam must be transmitted.